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1 /* Web construction code for GNU compiler.
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2 Contributed by Jan Hubicka.
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3 Copyright (C) 2001, 2002, 2004, 2006, 2007, 2008
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4 Free Software Foundation, Inc.
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5
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6 This file is part of GCC.
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7
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8 GCC is free software; you can redistribute it and/or modify it under
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9 the terms of the GNU General Public License as published by the Free
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10 Software Foundation; either version 3, or (at your option) any later
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11 version.
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12
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13 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
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14 WARRANTY; without even the implied warranty of MERCHANTABILITY or
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15 FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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16 for more details.
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17
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18 You should have received a copy of the GNU General Public License
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19 along with GCC; see the file COPYING3. If not see
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20 <http://www.gnu.org/licenses/>. */
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21
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22 /* Simple optimization pass that splits independent uses of each pseudo,
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23 increasing effectiveness of other optimizations. The optimization can
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24 serve as an example of use for the dataflow module.
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25
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26 We don't split registers with REG_USERVAR set unless -fmessy-debugging
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27 is specified, because debugging information about such split variables
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28 is almost unusable.
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29
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30 TODO
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31 - Add code to keep debugging up-to-date after splitting user variable
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32 pseudos. This can be done by keeping track of all the pseudos used
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33 for the variable and using life analysis information before reload
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34 to determine which one is live and, in case more than one are live,
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35 choose the one with the latest definition.
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36
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37 Other optimization passes can benefit from the infrastructure too.
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38
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39 - We may use profile information and ignore infrequent use for the
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40 purpose of web unifying, inserting the compensation code later to
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41 implement full induction variable expansion for loops (currently
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42 we expand only if the induction variable is dead afterward, which
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43 is often the case). */
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44
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45 #include "config.h"
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46 #include "system.h"
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47 #include "coretypes.h"
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48 #include "tm.h"
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49 #include "toplev.h"
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50
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51 #include "rtl.h"
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52 #include "hard-reg-set.h"
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53 #include "flags.h"
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54 #include "obstack.h"
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55 #include "basic-block.h"
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56 #include "output.h"
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57 #include "df.h"
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58 #include "function.h"
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59 #include "timevar.h"
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60 #include "tree-pass.h"
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61
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62
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63 static rtx entry_register (struct web_entry *, df_ref, char *);
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64 static void replace_ref (df_ref, rtx);
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65
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66 /* Find the root of unionfind tree (the representative of set). */
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67
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68 struct web_entry *
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69 unionfind_root (struct web_entry *element)
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70 {
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71 struct web_entry *element1 = element, *element2;
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72
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73 while (element->pred)
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74 element = element->pred;
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75 while (element1->pred)
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76 {
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77 element2 = element1->pred;
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78 element1->pred = element;
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79 element1 = element2;
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80 }
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81 return element;
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82 }
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83
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84 /* Union sets.
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85 Return true if FIRST and SECOND points to the same web entry structure and
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86 nothing is done. Otherwise, return false. */
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87
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88 bool
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89 unionfind_union (struct web_entry *first, struct web_entry *second)
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90 {
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91 first = unionfind_root (first);
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92 second = unionfind_root (second);
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93 if (first == second)
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94 return true;
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95 second->pred = first;
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96 return false;
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97 }
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98
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99 /* For each use, all possible defs reaching it must come in the same
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100 register, union them.
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101 FUN is the function that does the union. */
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102
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103 void
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104 union_defs (df_ref use, struct web_entry *def_entry,
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105 struct web_entry *use_entry,
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106 bool (*fun) (struct web_entry *, struct web_entry *))
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107 {
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108 struct df_insn_info *insn_info = DF_REF_INSN_INFO (use);
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109 struct df_link *link = DF_REF_CHAIN (use);
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110 df_ref *use_link;
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111 df_ref *eq_use_link;
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112 df_ref *def_link;
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113 rtx set;
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114
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115 if (insn_info)
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116 {
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117 rtx insn = insn_info->insn;
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118 use_link = DF_INSN_INFO_USES (insn_info);
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119 eq_use_link = DF_INSN_INFO_EQ_USES (insn_info);
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120 def_link = DF_INSN_INFO_DEFS (insn_info);
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121 set = single_set (insn);
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122 }
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123 else
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124 {
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125 /* An artificial use. It links up with nothing. */
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126 use_link = NULL;
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127 eq_use_link = NULL;
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128 def_link = NULL;
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129 set = NULL;
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130 }
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131
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132 /* Some instructions may use match_dup for their operands. In case the
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133 operands are dead, we will assign them different pseudos, creating
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134 invalid instructions, so union all uses of the same operand for each
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135 insn. */
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136
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137 if (use_link)
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138 while (*use_link)
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139 {
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140 if (use != *use_link
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141 && DF_REF_REAL_REG (use) == DF_REF_REAL_REG (*use_link))
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142 (*fun) (use_entry + DF_REF_ID (use),
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143 use_entry + DF_REF_ID (*use_link));
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144 use_link++;
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145 }
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146
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147 if (eq_use_link)
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148 while (*eq_use_link)
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149 {
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150 if (use != *eq_use_link
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151 && DF_REF_REAL_REG (use) == DF_REF_REAL_REG (*eq_use_link))
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152 (*fun) (use_entry + DF_REF_ID (use),
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153 use_entry + DF_REF_ID (*eq_use_link));
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154 eq_use_link++;
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155 }
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156
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157 /* Recognize trivial noop moves and attempt to keep them as noop. */
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158
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159 if (set
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160 && SET_SRC (set) == DF_REF_REG (use)
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161 && SET_SRC (set) == SET_DEST (set))
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162 {
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163 if (def_link)
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164 while (*def_link)
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165 {
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166 if (DF_REF_REAL_REG (use) == DF_REF_REAL_REG (*def_link))
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167 (*fun) (use_entry + DF_REF_ID (use),
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168 def_entry + DF_REF_ID (*def_link));
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169 def_link++;
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170 }
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171 }
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172 while (link)
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173 {
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174 (*fun) (use_entry + DF_REF_ID (use),
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175 def_entry + DF_REF_ID (link->ref));
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176 link = link->next;
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177 }
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178
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179 /* A READ_WRITE use requires the corresponding def to be in the same
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180 register. Find it and union. */
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181 if (DF_REF_FLAGS (use) & DF_REF_READ_WRITE)
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182 {
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183 df_ref *link;
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184
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185 if (insn_info)
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186 link = DF_INSN_INFO_DEFS (insn_info);
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187 else
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188 link = NULL;
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189
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190 if (link)
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191 while (*link)
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192 {
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193 if (DF_REF_REAL_REG (*link) == DF_REF_REAL_REG (use))
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194 (*fun) (use_entry + DF_REF_ID (use),
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195 def_entry + DF_REF_ID (*link));
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196 link++;
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197 }
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198 }
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199 }
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200
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201 /* Find the corresponding register for the given entry. */
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202
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203 static rtx
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204 entry_register (struct web_entry *entry, df_ref ref, char *used)
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205 {
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206 struct web_entry *root;
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207 rtx reg, newreg;
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208
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209 /* Find the corresponding web and see if it has been visited. */
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210 root = unionfind_root (entry);
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211 if (root->reg)
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212 return root->reg;
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213
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214 /* We are seeing this web for the first time, do the assignment. */
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215 reg = DF_REF_REAL_REG (ref);
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216
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217 /* In case the original register is already assigned, generate new one. */
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218 if (!used[REGNO (reg)])
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219 newreg = reg, used[REGNO (reg)] = 1;
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220 else if (REG_USERVAR_P (reg) && 0/*&& !flag_messy_debugging*/)
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221 {
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222 newreg = reg;
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223 if (dump_file)
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224 fprintf (dump_file,
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225 "New web forced to keep reg=%i (user variable)\n",
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226 REGNO (reg));
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227 }
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228 else
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229 {
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230 newreg = gen_reg_rtx (GET_MODE (reg));
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231 REG_USERVAR_P (newreg) = REG_USERVAR_P (reg);
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232 REG_POINTER (newreg) = REG_POINTER (reg);
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233 REG_ATTRS (newreg) = REG_ATTRS (reg);
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234 if (dump_file)
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235 fprintf (dump_file, "Web oldreg=%i newreg=%i\n", REGNO (reg),
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236 REGNO (newreg));
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237 }
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238
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239 root->reg = newreg;
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240 return newreg;
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241 }
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242
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243 /* Replace the reference by REG. */
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244
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245 static void
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246 replace_ref (df_ref ref, rtx reg)
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247 {
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248 rtx oldreg = DF_REF_REAL_REG (ref);
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249 rtx *loc = DF_REF_REAL_LOC (ref);
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250 unsigned int uid = DF_REF_INSN_UID (ref);
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251
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252 if (oldreg == reg)
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253 return;
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254 if (dump_file)
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255 fprintf (dump_file, "Updating insn %i (%i->%i)\n",
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256 uid, REGNO (oldreg), REGNO (reg));
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257 *loc = reg;
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258 df_insn_rescan (DF_REF_INSN (ref));
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259 }
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260
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261
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262 static bool
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263 gate_handle_web (void)
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264 {
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265 return (optimize > 0 && flag_web);
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266 }
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267
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268 /* Main entry point. */
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269
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270 static unsigned int
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271 web_main (void)
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272 {
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273 struct web_entry *def_entry;
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274 struct web_entry *use_entry;
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275 unsigned int max = max_reg_num ();
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276 char *used;
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277 basic_block bb;
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278 unsigned int uses_num = 0;
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279 rtx insn;
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280
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281 df_set_flags (DF_NO_HARD_REGS + DF_EQ_NOTES);
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282 df_chain_add_problem (DF_UD_CHAIN);
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283 df_analyze ();
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284 df_set_flags (DF_DEFER_INSN_RESCAN);
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285
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286 /* Assign ids to the uses. */
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287 FOR_ALL_BB (bb)
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288 FOR_BB_INSNS (bb, insn)
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289 {
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290 unsigned int uid = INSN_UID (insn);
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291 if (INSN_P (insn))
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292 {
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293 df_ref *use_rec;
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294 for (use_rec = DF_INSN_UID_USES (uid); *use_rec; use_rec++)
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295 {
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296 df_ref use = *use_rec;
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297 if (DF_REF_REGNO (use) >= FIRST_PSEUDO_REGISTER)
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298 DF_REF_ID (use) = uses_num++;
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299 }
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300 for (use_rec = DF_INSN_UID_EQ_USES (uid); *use_rec; use_rec++)
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301 {
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302 df_ref use = *use_rec;
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303 if (DF_REF_REGNO (use) >= FIRST_PSEUDO_REGISTER)
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304 DF_REF_ID (use) = uses_num++;
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305 }
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306 }
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307 }
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308
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309 /* Record the number of uses and defs at the beginning of the optimization. */
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310 def_entry = XCNEWVEC (struct web_entry, DF_DEFS_TABLE_SIZE());
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311 used = XCNEWVEC (char, max);
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312 use_entry = XCNEWVEC (struct web_entry, uses_num);
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313
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314 /* Produce the web. */
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315 FOR_ALL_BB (bb)
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316 FOR_BB_INSNS (bb, insn)
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317 {
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318 unsigned int uid = INSN_UID (insn);
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319 if (INSN_P (insn))
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320 {
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321 df_ref *use_rec;
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322 for (use_rec = DF_INSN_UID_USES (uid); *use_rec; use_rec++)
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323 {
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324 df_ref use = *use_rec;
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325 if (DF_REF_REGNO (use) >= FIRST_PSEUDO_REGISTER)
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326 union_defs (use, def_entry, use_entry, unionfind_union);
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327 }
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328 for (use_rec = DF_INSN_UID_EQ_USES (uid); *use_rec; use_rec++)
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329 {
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330 df_ref use = *use_rec;
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331 if (DF_REF_REGNO (use) >= FIRST_PSEUDO_REGISTER)
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332 union_defs (use, def_entry, use_entry, unionfind_union);
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333 }
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334 }
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335 }
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336
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337 /* Update the instruction stream, allocating new registers for split pseudos
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338 in progress. */
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339 FOR_ALL_BB (bb)
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340 FOR_BB_INSNS (bb, insn)
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341 {
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342 unsigned int uid = INSN_UID (insn);
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343 if (INSN_P (insn))
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344 {
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345 df_ref *use_rec;
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346 df_ref *def_rec;
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347 for (use_rec = DF_INSN_UID_USES (uid); *use_rec; use_rec++)
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348 {
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349 df_ref use = *use_rec;
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350 if (DF_REF_REGNO (use) >= FIRST_PSEUDO_REGISTER)
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351 replace_ref (use, entry_register (use_entry + DF_REF_ID (use), use, used));
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352 }
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353 for (use_rec = DF_INSN_UID_EQ_USES (uid); *use_rec; use_rec++)
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354 {
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355 df_ref use = *use_rec;
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356 if (DF_REF_REGNO (use) >= FIRST_PSEUDO_REGISTER)
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357 replace_ref (use, entry_register (use_entry + DF_REF_ID (use), use, used));
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358 }
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359 for (def_rec = DF_INSN_UID_DEFS (uid); *def_rec; def_rec++)
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360 {
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361 df_ref def = *def_rec;
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362 if (DF_REF_REGNO (def) >= FIRST_PSEUDO_REGISTER)
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363 replace_ref (def, entry_register (def_entry + DF_REF_ID (def), def, used));
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364 }
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365 }
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366 }
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367
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368 free (def_entry);
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369 free (use_entry);
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370 free (used);
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371 return 0;
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372 }
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373
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374 struct rtl_opt_pass pass_web =
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375 {
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376 {
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377 RTL_PASS,
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378 "web", /* name */
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379 gate_handle_web, /* gate */
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380 web_main, /* execute */
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381 NULL, /* sub */
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382 NULL, /* next */
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383 0, /* static_pass_number */
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384 TV_WEB, /* tv_id */
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385 0, /* properties_required */
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386 0, /* properties_provided */
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387 0, /* properties_destroyed */
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388 0, /* todo_flags_start */
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389 TODO_df_finish | TODO_verify_rtl_sharing |
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390 TODO_dump_func /* todo_flags_finish */
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391 }
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392 };
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393
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